That could be the problem as both in XP and Vista there is an Admin account, the users of one aren’t recognized by the other, etc.
The operational system always work, wanting you or not… It creates System Volume Information folder (System Restore), a different Recycle Bin folder, etc.
Fully agree, I’m astonished too…
Look, this is easy for M$ to say… avast will detect a tmp file as infected IF it is infected, not by the reason of being temporary…
Although, I can’t imagine how to help you further… The FAT32 system shouldn’t have access problems by both OS.